Scott Kelly and Kjell Lindgren from the US space agency NASA started the endeavour at 8.03 a.m., which was expected to last six hours and 30 minutes, NASA said.

The first task for the duo will be to install a thermal cover on the Alpha Magnetic Spectrometer, which is a state-of-the-art particle physics detector that has been attached to the station since 2011.They will also lubricate the 57.7-foot Canadarm2 robotic arm, remove a piece of thermal insulation from a power switching unit, and route power cables for a future docking port.

This was the 32nd US spacewalk to service the station, but it is the first for both Kelly, who is in the middle of a year-long mission aboard the station, and flight engineer Lindgren.Another spacewalk is scheduled for the pair on November 6. in an attempt to restore an ammonia cooling system to its original configuration.

A spacewalk was conducted in November 2012 to try to isolate a leak in the station's cooling supply, but the leak was subsequently traced to a different component.